Hereto, in order to enable high-density mounting of electronic circuits, a stack structure has been used wherein a plurality of printed circuit boards (PCBs) are oppositely placed to each other and the printed circuit boards are connected by stack connectors or the like. While the stack structure may implement high-density mounting of electronic circuits, heat generating elements are prone to be densely packed therein. Therefore, the cooling of the heat generating elements is a problem.
For the cooling of the heat generating elements, a method is generally used wherein plate fins, pin fins, or the like are arranged on surfaces of the heat generating elements. Also used a method wherein forced air cooling is performed by generating air flows around the fins by using a fan. Furthermore, there is a disclosure of heat radiators that are disposed between heat generating elements are oppositely placed between printed circuit boards, and that simultaneously cools the heat generating elements. For example, refer to the Japanese Laid-open Patent Publication No. 2006-319134 and Japanese Laid-open Patent Publication No. 2006-202975.
In the above-described prior art, however, there is a problem that it is difficult to install the heat radiator between the printed circuit boards oppositely placed. For example, when using a heat sink having a plate heat radiation fin, the height of the heat radiation fin is limited by the distance between the printed circuit boards. Therefore, height of the heat radiation fins is adjusted in accordance with the distance between the printed circuit boards.
Moreover, heights of the heat generating elements mounted on the printed circuit boards are different from one another, the height of the heat radiation fins is adjusted in accordance with the height of a heat generating element having a heat sink. In particular, when heat generating elements are oppositely placed between printed circuit boards, there is a problem that heat radiation fins as heat sinks to be installed to respective heat generating elements may collide with one another to thereby make it impossible for the heat radiation fins to be easily installed.
Furthermore, when graphite sheets are used of the Japanese Laid-open Patent Publication No. 2006-319134. There is an absence of a sufficient space between the printed circuit boards because the graphite sheets are provided between printed circuit boards in a packed manner. As a result, a method such as forced air cooling cannot be used, which causes a problem that a cooling effect with respect to heat generating elements cannot be sufficiently obtained. Moreover, because the graphite sheets have low elasticity, there occurs a need to make an adjustment of height in accordance with a distance between the printed circuit boards and a height of heat generating element.